Is it correct to say: Confusing ethanol (C₂H₅OH) with ethanoic acid (CH₃COOH)?

Ethanol has -OH; ethanoic acid has -COOH. Ethanol is neutral; ethanoic acid is a weak acid (pH ~ 3).

Is it correct to say: Writing the wrong functional group during nomenclature?

-OH → -anol; -COOH → -anoic acid; -CHO → -anal; -CO- → -anone. Learn the suffix table.

Is it correct to say: Saying methane and ethane are unsaturated?

Alkanes are SATURATED (only single bonds). Unsaturated = has C=C (alkene) or C≡C (alkyne).

Is it correct to say: Drawing structural isomers of propane (C₃H₈)?

Propane has NO isomer. Structural isomerism starts at BUTANE (C₄H₁₀) → n-butane, iso-butane.

Is it correct to say: Forgetting to write 'conc.' before H₂SO₄ in esterification / dehydration?

Concentration matters — dilute H₂SO₄ is just an acid; concentrated is a strong dehydrating agent.

Is it correct to say: Explaining scum as 'soap-water not mixing'?

Soap DOES mix with water. Scum arises from Ca²⁺ / Mg²⁺ ions in HARD water reacting with the soap anion to form an insoluble salt.

Carbon and its Compounds

Tetravalency of carbon, allotropes, hydrocarbons, functional groups, ethanol and ethanoic acid, soaps — NCERT Class 10 Chemistry Ch 4

📐 10 formulas✏️ 3 examples🎯 6 practice⚖️ 6 marks🏫 CBSE📚 Class 10✓ 2025–26 syllabus

💡

Board Exam Tips

→Structural formulae of first four alkanes/alkenes/alkynes — draw with hydrogen atoms visible.
→Reactions of ethanol (dehydration with conc. H₂SO₄; oxidation with alkaline KMnO₄) and ethanoic acid (esterification, reaction with Na, NaOH, Na₂CO₃) — each is 2-3 marks.
→Soap vs detergent — a favourite 3-mark comparison. Also 'why soaps do not clean in hard water'.
→Structural isomerism appears from butane (C₄H₁₀) onward. Draw both isomers.
→Micelle diagram — draw the hydrophobic tail + hydrophilic head clearly.

📐 Formulas(10)

General Formula of Alkane★ Board fav

C_{n} H_{2 n + 2}

General Formula of Alkene

C_{n} H_{2 n}

General Formula of Alkyne

C_{n} H_{2 n - 2}

Combustion of Ethanol

C_{2} H_{5} O H + 3 O_{2} ⟶ 2 C O_{2} + 3 H_{2} O + heat

Dehydration of Ethanol★ Board fav

C_{2} H_{5} O H conc. H_{2} S O_{4}, 17 0^{\circ} C C_{2} H_{4} + H_{2} O

Oxidation of Ethanol

C_{2} H_{5} O H alk. K M n O_{4} /Δ C H_{3} C O O H

Esterification★ Board fav

C H_{3} C O O H + C_{2} H_{5} O H conc. H_{2} S O_{4} C H_{3} C O O C_{2} H_{5} + H_{2} O

Ester + NaOH (Saponification)

C H_{3} C O O C_{2} H_{5} + N a O H ⟶ C H_{3} C O O N a + C_{2} H_{5} O H

Ethanoic Acid + Sodium Bicarbonate

C H_{3} C O O H + N a H C O_{3} ⟶ C H_{3} C O O N a + H_{2} O + C O_{2} (g)

Soap (Long Chain Sodium Salt)

C_{17} H_{35} C O O N a

✏️ Solved Examples

1Solved Exampleeasy3 steps

Draw the electron-dot structure of methane (CH₄) and state the geometry.

Carbon has 4 valence electrons; each H has 1. Each C-H bond is a shared pair.

2Solved Exampleboard4 steps

What happens when ethanoic acid reacts with (a) sodium metal, (b) sodium carbonate, (c) ethanol in the presence of conc. H₂SO₄? Write equations.

(a) Acidic H replaced by Na, H₂ evolved

2 C H_{3} C O O H + 2 N a ⟶ 2 C H_{3} C O O N a + H_{2}

3Solved ExampleHOTS4 steps

Explain, with a labelled diagram of a micelle, why soap cleans an oily cloth but fails to clean it in hard water.

Soap molecule = long hydrocarbon tail (hydrophobic) + -COO⁻Na⁺ head (hydrophilic).

⚠️ Traps & Common Mistakes

⚠️Common Mistakes6

1
Confusing ethanol (C₂H₅OH) with ethanoic acid (CH₃COOH)
✓Ethanol has -OH; ethanoic acid has -COOH. Ethanol is neutral; ethanoic acid is a weak acid (pH ~ 3).
2
Writing the wrong functional group during nomenclature
✓-OH → -anol; -COOH → -anoic acid; -CHO → -anal; -CO- → -anone. Learn the suffix table.
3
Saying methane and ethane are unsaturated
✓Alkanes are SATURATED (only single bonds). Unsaturated = has C=C (alkene) or C≡C (alkyne).
4
Drawing structural isomers of propane (C₃H₈)
✓Propane has NO isomer. Structural isomerism starts at BUTANE (C₄H₁₀) → n-butane, iso-butane.
5
Forgetting to write 'conc.' before H₂SO₄ in esterification / dehydration
✓Concentration matters — dilute H₂SO₄ is just an acid; concentrated is a strong dehydrating agent.
6
Explaining scum as 'soap-water not mixing'
✓Soap DOES mix with water. Scum arises from Ca²⁺ / Mg²⁺ ions in HARD water reacting with the soap anion to form an insoluble salt.

🎯 Practice Yourself

🎯Practice Yourself6 questions

Q1
Write the molecular and structural formulae of the first three members of the alkane homologous series.
Q2
Give the IUPAC names of (a) CH₃CH₂OH, (b) CH₃COOH, (c) HCHO, (d) CH₃COCH₃.
Q3
Distinguish between soap and detergent (any three differences).
Q4
What is meant by denatured alcohol? Why is it done?
Q5
How would you distinguish ethanol from ethanoic acid using two chemical tests?
Q6
Give two uses of ethanoic acid.

📝 Notes

Carbon and its Compounds

Carbon is the backbone of life — 30 million+ carbon compounds are known, more than for all other elements combined.

Why carbon is special

Tetravalency: 4 valence electrons ⇒ 4 covalent bonds ⇒ vast bonding possibilities.
Catenation: ability to link with itself in chains, branches and rings — nearly unlimited chain lengths.
Small size ⇒ strong bonds: C-C and C-H bonds are strong and stable to heat/attack.

Allotropes to remember

| Allotrope | Bonding | Property | |---|---|---| | Diamond | Tetrahedral 3D network | Hardest natural substance, insulator | | Graphite | Layered hexagons, delocalised π | Soft, conducts electricity | | Buckminsterfullerene (C₆₀) | Football-cage | Semiconductor, novel electronics |

Homologous series

A family of compounds with the same general formula, similar chemistry, and each successive member differs by −CH₂− (14 u).

Alkane CₙH₂ₙ₊₂ — CH₄, C₂H₆, C₃H₈…
Alkene CₙH₂ₙ — C₂H₄, C₃H₆…
Alkyne CₙH₂ₙ₋₂ — C₂H₂, C₃H₄…
Alcohol CₙH₂ₙ₊₁OH — CH₃OH, C₂H₅OH…
Carboxylic acid CₙH₂ₙ₊₁COOH — HCOOH, CH₃COOH…

Functional groups — the "handles" of chemistry

| Group | Formula | Suffix / Prefix | |---|---|---| | Alcohol | -OH | -anol | | Aldehyde | -CHO | -anal | | Ketone | >C=O | -anone | | Carboxylic acid | -COOH | -anoic acid | | Halogen | -X (F, Cl, Br, I) | halo- (prefix) | | Double / triple bond | C=C / C≡C | -ene / -yne |

Soap — how it cleans

Soap is amphipathic: tail loves grease, head loves water. In water, molecules aggregate into micelles with the tail packed inside and head outside. Micelles trap oily dirt and are washed away by water.

Quick sanity checks

Combustion of any hydrocarbon: full oxidation gives CO₂ + H₂O + heat.
Ethanol test: colour change of hot orange K₂Cr₂O₇/H⁺ from orange → green (also alk. KMnO₄ decolorises).
Carboxylic acid test: effervescence with NaHCO₃.